TDS3012B blank screen

[AlcidePiR2]

Dear All,

I had started this repair of a TDS3012B nearly four years ago, but did not succeed.  I checked the power supply, but this is fine.

The problem is the blank screen ( although lighted)



When I saw the new thread
https://www.eevblog.com/forum/repair/tds3014-adventures-(seeking-75-75mhz-oscillator)/

I had some hope. I  just checked the 75 Mhz and 48 Mhz oscillators, but unfortunately, boith are fine and provide the desired signal.

I  am  thus back in the darkness and will appreciate any suggestions.

[AlcidePiR2]

As you can see, I have made a very delicate investigation on the DS1742W chip to check the residual voltage of the battery.

Previously, I had  attaked such chip by the bottom. This time I did it from the top.

I used a magnet to search where was the battery, and then used a drill.
The problem on the top is that you access first the - side of the battery which is connected to the ground.

You have then to dig a little bit more to get the +  side of the battery.
I found 2.89 V  which  is very fine and should not be a problem. So  the fault should not come from this chip.

[james_s]

The scope will boot with the DS1742 battery dead, I don't think that is your problem. When I was working on mine I tried installing a plain 6116 SRAM chip in its place and everything worked fine except the time would not advance and all settings were lost when the scope powered off.

[AlcidePiR2]

Maybe this could help to localize the problem. I have checked that there is no signal at the front panel  square signal test.

[james_s]

I don't know about the TDS series but in most Tek scopes the probe calibration oscillator is a separate circuit that only requires power. Have you checked the power rails? The main power supply puts out 15V and then on the main board there are more regulators to get 3.3V and other voltages used.

[madao]

Did reponse  frontplate , or flashing  LED while bootup?


If  yes ->  check   TFT & Cable.

greetings
matt

[AlcidePiR2]

Did reponse  frontplate , or flashing  LED while bootup?


If  yes ->  check   TFT & Cable.

No flashing leds when I turn it on .

[AlcidePiR2]

I have now totally dismounted the scope.

The power supply boards ( main and battery) seems to be OK, as I have ( I think )  the right stable  voltages at the J100/J200 connectors
( 5.17 V  and 14.56 V ).

If I connect A, B, and C,  (see pic) the board powers, but no led lights on the front panel, and no signal at the  1khz test point. Although the voltages
seems OK  at the BNC connector  ( except a 5 V offset, probably due to the fact that the GND of the  BNC is not connected to the GND of the
board.  The board  get powered just a few seconds, and then shuts down.

By the way, how is  the GND of the BNC connector  conneccted to the GND of the board ?  Is it  through the chassi ?






Rant :  I  had only  the TDS3000  maintenance manual which is already quite limited. I finally get hold on a TDS300B maintenance manual.
http://www.pewa.de/DATENBLATT/DBL_TEK_TDS3000-SERVICE-MANUAL_ENGLISCH.PDF

I expectred I could have found there more information related to my specific model, but this manual is a joke.
They removed all technical parts. The only thing a technician is allowed to do is to replace the main power supply board. For anything else, go to
Tektronix.

[james_s]

Yes that is easily the biggest problem with the TDS3000 series of otherwise excellent scopes. The documentation is a joke, there is no serious technical/service information at all.

[rvalente]

Yes that is easily the biggest problem with the TDS3000 series of otherwise excellent scopes. The documentation is a joke, there is no serious technical/service information at all.

Hello, is there any troubleshooting for this problem? A few post says about reballing/reflowing the 68K power PC bga

https://www.eevblog.com/forum/testgear/200usd-on-a-broken-tds3034b-is-it-worth/msg3579048/#msg3579048

https://forum.tek.com/viewtopic.php?t=138040

[pcarew]

Hello AlcidePiR2,
I realize that it has been a couple of years, but did you make any further progress with you Tek scope?

I have a TDS3054B with *exactly* the same symptoms as yours. I have checked the power supply voltages etc and I also don't have a square wave test signal.

This scope was working, but hasn't been powered on for 3-4 years. When I went to use it again, it was dead (with the exception of the fan and screen backlight)
Best
Paul.

[pcarew]

Hello AlcidePiR2,
I've progressed the diagnosis of my dead TDS3000 to where I think it might be the processor (either dead or broken BGA connection).
I have started a new thread dealing with that:

https://www.eevblog.com/forum/repair/dead-tds3000b-(3054b)-possibly-processor/

[pcarew]

Well I know it has been nearly 2 years since I last posted on this thread, but I *finally* got around to removing/replacing the Motorola Processor BGA.
I replaced the chip with a new one purchased from Motorola/NXP

And.....drum roll.... **No Change** :-( :-(

Same symptoms, blank screen with white back light and fan running, no other activity

So after all this time, I think that was a 'red herring'

Hmmmm....

So, back to the drawing board so to speak

[meduza]

Check the bus, maybe there's somewhere a short between address/data pins. I recommend you inspect pins of memory chips with a microscope, check adjacent pins for shorts, and check the bus activity on all address and data pins.

[coromonadalix]

was there a 25Mhz  oscillator diying  who could block the boot process ??